Rotating electrical machines, such as motors and generators, have a rotor and a stator that are magnetically coupled. Generally, the rotor has a coil that is used to produce a magnetic field. In particular, electricity flowing through the rotor coil produces the magnetic field. In a generator, the rotor is coupled to a prime mover that rotates the rotor, producing a rotating magnetic field that induces a voltage in the stator. The voltage produced in the stator is used to supply power to an electrical grid. Alternately, in a motor, the stator produces a rotating magnetic field that interacts with the magnetic field produced by the rotor coil to induce rotation of the rotor.
Conventional copper conductors are commonly used to form the rotor coils. However, the electrical resistance of copper is sufficient to produce a substantial amount of resistant heat loss in the rotor coil, which reduces the efficiency of the rotating machine. In response to the losses caused by conventional copper conductors, superconductors have been developed for use as rotor coils. A superconductor is a material that loses its electrical resistance below a predetermined transition temperature, making it desirable for use as a rotor coil.
In a rotating machine utilizing a superconductive rotor coil, the rotor coil is cooled by a cryogenic fluid to lower the temperature of the superconductive coil below the transition temperature. Below the transition temperature, the superconductive rotor coil enters a superconductive state and loses its electrical resistance. Generally, a cryogenic fluid is provided to the superconductive coil by an external source of cryogenic fluid. The cryogenic fluid absorbs heat from the superconductive rotor coil, which maintains the rotor coil below the transition temperature and in the superconductive state. The cryogenic fluid for cooling the superconductive rotor coil is transferred between the source of cryogenic fluid and the rotor by a transfer coupling located at one end of the rotor shaft.
However, a number of problems are associated with transferring cryogenic fluid through the end of the rotor shaft. For example, a generator may be disposed between two turbines. In this configuration, neither end of the rotor shaft is accessible to supply cryogenic fluid to the rotor coil.
Thus, there is a need for improved device for conveying a coolant fluid to a rotating device.